In recent years, a mobile phone which is equipped with wireless LAN (Local Area Network) function begins to appear on the market. A mobile phone which is equipped with wireless LAN function can be connected with a mobile telephone network such as an IMT (International Mobile Telecommunication)-2000 network and a wireless LAN.
Here, in data communication via an IMT-2000 network, in order that traffic of a network will not become full, the upper limit of a file size allowable for data communication is decided. Accordingly, a user cannot download a large capacity file with a file size exceeding the upper limit. Further, when sending or receiving a file of particular contents with a relatively large capacity, the communication speed of data communication via an IMT-2000 network is slower than the communication speed of data communication via a wireless LAN, and efficiencies are low.
In Japanese Patent Application Laid-Open No. 2004-336256, a data communication system which changes a bearer in such a case when the fall of the radio field intensity during data communication with a server device such as a contents server is detected is disclosed. In the data communication system, a terminal device and a mobile terminal are connected with a TCP (Transmission Control Protocol)/IP (Internet Protocol) network respectively. In this state, the terminal device downloads contents from a contents server via a mobile terminal, an IMT-200 network and a TCP/IP network. Then, when a fall of the radio field intensity is detected during downloading, the mobile terminal disconnects the connection with the IMT-200 network. At that time, because a connection of the terminal device and the TCP/IP network is continued, communication between the contents server and the TCP/IP network is maintained. So, contents transmitted to the TCP/IP network from the contents server are stored in a proxy server until the mobile terminal establishes communication newly. Contents stored in the proxy server are downloaded to the terminal device via the wireless LAN and the mobile terminal, when the mobile terminal establishes communication with a wireless LAN.
Also in Japanese Patent Application Laid-Open No. 2006-155506, a contents supply method which provides contents considering the types of bearers that a mobile terminal uses is disclosed. In the contents supply method, when a server receives a transmission request of contents from a mobile terminal, contents suitable for the bearer are selected based on the bearer's information used by the transmission request of contents. Then, for the transmission request of contents, selected contents are transmitted to the mobile terminal. Accordingly, by applying the contents supply method, it is possible to transmit contents suitable for a bearer.